Recently, destruction of the ozone layer that acts as a barrier layer protecting against ultraviolet rays from the sun has been occurring along with the progression of global scale environmental changes. As a result, the bare skin of people has become exposed to strong ultraviolet (UV) rays from the sun. These UV rays include high amounts of energy and have a variety of harmful effects on the skin. Thus, attention has focused on the function of UV ray protection agents that are used for sun care protection of the skin against harmful UV rays.
As people go about their everyday lives their skin is often exposed, regardless of whether they are indoors or outside. In particular, when working outside or doing sports, leisure activities or the like, people have a tendency to expose their skin for various reasons, such as to attain a feeling of coolness (to cool the skin) or a feeling of freedom. As a result, there is a danger that people will expose their skin to harmful UV rays from the sun throughout the year.
In order to protect against the danger of skin cancer developing and harmful reactions of the body (said to be a cause of skin aging) caused by exposure to the UV rays, cosmetic products are used (for example, sunscreen creams) made of compounds of UV ray protection agents. The UV ray protection agents that are used as compounds in these types of cosmetic product can be broadly classified as being either organic type UV ray protection agents or inorganic type UV ray scattering agents.
Organic type UV ray protection agents have conjugated double bonds in their molecules. This type of molecule absorbs the light energy of the UV rays, and changes it in to a different form of energy like heat energy. If the molecular structure of the agent is changed, the wave length of the UV rays that are maximally absorbed changes (the maximum absorption wavelength). As a result, organic type UV protection agents are classified based on the difference in the UV ray absorption region that they are intended to absorb, namely, as UVB absorption agents that absorb UV rays with a comparatively short wavelength (maximum absorption wavelength of 280 to 320 nm), and UVA absorption agents that absorbs UV rays with a comparatively long wavelength (maximum absorption wavelength of 320 to 400 nm).
On the other hand, inorganic type UV ray scattering agents are metallic oxides, most famously represented by titanium dioxide, that scatter the UV rays with their high refractive index.
However, inorganic type UV ray scattering agents epitomized by titanium dioxide generally have a color from white to light yellow, and act so as to strongly conceal the surface of the object to which they are applied. Accordingly, for example, if a sunscreen cream or the like including inorganic type UV ray scattering agent is applied to the skin to protect against sunburn, the skin becomes an unnatural color with a white tone. Thus, for example, if a person wishes to protect against sunburn but wishes to avoid having an unnatural white toned skin color, it is difficult to use large quantities of just an inorganic type UV ray scattering agent.
In contrast to this, organic type UV ray protection agents are generally colorless, or have a slight coloring. They either have no concealing effect on the surface of the object to which they are applied, or have a concealing effect that can be ignored.
Accordingly, if a person wishes to protect their skin against the harmful action of UV rays while also avoiding their skin from becoming an unnatural white toned color, it is desirable to use either an organic type UV ray protection agent or a compound including a favorable mixing ratio of an organic type UV ray protection agent and an inorganic type UV ray scattering agent.
Organic type UV ray protection agents have the advantage that it is possible to obtain different UV ray protection effects for different uses by changing the molecular structure thereof.
At present, p-methoxycinnamic acid-2-ethyl hexyl and 4-tert-butyl4′-methoxy-dibenzoylmethane are widely used, respectively, as UVB absorption agent and UVA absorption agent.
However, conventional organic type UV ray protection agents like this generally have a strong skin irritant effect and acute toxicity. Since UV ray protection agents are usually used by spreading them over a large area of the skin, it is preferable that skin irritant effect and acute toxicity are as low as possible. Moreover, bearing in mind the recent increase in the amount of UV rays from the sun, a substantial increase in the UV ray protection performance of UV ray protection agents is desirable. Further, the UV ray protection agent is exposed to direct sunlight over a long period after it has been applied to the skin, and thus it is important that it has high resistance to decomposition by light and heat.
Based on a general assessment of all these matters, it is clear that conventional UV ray protection agents still have inadequate performance for their role as UV ray protection agents. Accordingly, there is strong need for development of: a new compound with low toxicity (for example, skin irritation effect and acute toxicity) to the body, a high degree of safety, strong maximum absorption in the UVB region and the UVA region, and high resistance to decomposition by light and heat; and a new UV protection agent containing a compound (including the new compound) that has a UV ray protection effect as an active ingredient.